The present invention relates to a novel process for the production of cement clinker from fuel shale, or other argillaceous and/or calcareous materials. The practice of the invention will be illustrated with respect to carbonaceous shale, such as oil shale or coal shale, but it is to be understood that it is not to be considered as limited thereto, but is applicable to a variety of calcareous and argillaceous raw materials commonly employed for the production of cement clinker, such as clay, blast furnace slag, and mixtures thereof with limestone or marl.
It is known that disintegrable combustible materials having a high mineral content, such as oil shale or coal shale, can be burned in specially designed steam boiler plants to produce heat and/or electric power. In the design of such boiler plants, special consideration must be given to the properties of the fuel, such as a lower heat load transfer rate per unit of area and the need for mechanical cleaning to remove materials which tend to deposit, such as lime, clay, and the like.
Whereas the fuel shale can be disintegrated to the required small particle size in grinding units, such as ball mills, these do not sufficiently change the structure of the material. The ash and slag which are produced in the combustion give rise to severe problems regarding ecological pollution because dry ash is blown off by the wind unless the ash dumps are continually moistened, and because they may contaminate underground water supplies.
It is known that the combustion of fuel shales in steam boiler plants can be improved in its overall economy by first subjecting the dry fuel shale to mechanical disintegration in a pin-type disintegrator in which the particles formed are subjected to repeated acceleration and retardation within a very short time interval of the order of fractions of a second, thereby homogenizing and activating at least a part of the shale, and a process of this type is disclosed in U.S. Pat. No. 3,972,724. It permits yields of 50% and more cement clinker in the combustion ash.
The ash and the cement clinker have to be separated in a further operation. Consequently, part of the combustion residue is waste, since the combustion ash cannot be effectively transformed into cement clinker.
Furthermore, oil shale, the inorganic component of which is suitable as a starting material for the production of cement clinker has been employed for this purpose in various prior art methods involving the separation of the organic from the inorganic components, so as to utilize the organic components economically for the production of energy, or at least removing them in a way not detrimental to the environment, and at the same time endeavoring to convert the inorganic components into cement clinker of the desired properties. Such methods have included subjecting the comminuted and granulated oil shale to a low temperature process to volatilize the organic components or to burn them, e.g. in a fluidized bed. The heat can be used to generate steam.
These known methods had, however, several disadvantages, such as that the quality of the final products obtained, i.e., the cement clinker, varied widely, and these variations were scarcely influenced by the manner of the heat treatment.
It is also known from said U.S. Pat. No. 3,972,724, that in the combustion of the oil shale, the residue could be separated, owing to differences in specific gravity, into cement clinker material on one hand, and ash and slag on the other hand, for example by centrifuging, and then the cement clinker portion could be considerably improved in its properties by subjecting it to a mechano-chemical process of activation in suitable disintegrators, to produce an increase in its chemical reactivity.